Manufacture of alternating current rectifiers of the dry-contact type



Patented Aug. 8, 1939 MANUFACTURE or auraana'rme enannu'r nee-muses or run ar-coarser TYPE Albert Leslie Williams and Leslie Ernest Thompson, London, England, assignors, by means: assignments, toUnion Switch & Signal Cornlll S Pa... a corporation of Pennsylvania No Drawing. Application July 23, 1938, Serial No. 221,004: In Great Britain July 2'1. 103'! 4 Claims. (Cl. 115-366) This invention relates to the manuiacture of alternating current rectifiers or the dry contact type and more particularly to the treatment of the selenium or analogous element utilised in rectifiers of this type in order to effect the conversion of the element from its original amorphous state into a metallicstate in which it a relatively high electric conductivity.

It has hitherto been usual to subject the selenium in the amorphous state after being applied to a base plate of suitable metallic material to a heat treatment at a temperature of from about 80 C. to the melting point of selenium (approximately 215 C.) and preferably exceeding 173 C. in order to effect the conversion of the selenium into the desired metallic and electrically conducting state.

According to the present invention the selenium or analogous element is, for attaining this purpose, subjected to a cooling treatment preferably at a temperature of approximately -60 C.

This cooling treatment may be employed if desired after a preliminary heat treatment of the element in its amorphous state in order to initiate or to effect the conversion into its metallic state, the cooling treatment completing the conversion or eflecting the final conversion of the element into an electrically conducting condition.

In carrying the invention into practice, a layer of selenium may be applied by melting or spraying on to a base plate at a temperature of approximately C. to C. above the melting point of selenium, the surface of the base plate being previously suitably roughened to ensure satisfactory adhesion of the selenium layer.

. This layer is then rendered compact and its surface flattened by the application of pressure while hot or when subsequently reheated to a temperature of approximately 90 C., the surface of the selenium layer during this stage of treatment being protected by a layer of some nonadhesive material such for example as aluminium foil.

The layer of selenium in its amorphous state is then converted into the metallic state by heating at-a temperature of approximately 130 C., pressure being applied to the rectifier blank during this stage to prevent distortion.

The conversion of the selenium into the final electrically conducting condition is then effected by subjecting the blank to intense cooling at a temperature of approximately C., after which the manufacture of the rectifier is completed by applying a conducting layer of a fusible metal or alloy to the surface of theselenium.

scribed by way of example.

The length of time during which the element must be maintained at the low temperature to effect the desired conversion does not appear to be criticaL'and tests indicate that an element which has been maintained at the low temperature for a period of two hours produces satisfactory results. The rate at which the element is restored to room temperature after the coolin step does not appear to affect the results obtained.

It will be understood that the selenium employed may contain other substances such as sulphur or may be in a combined form and that although particularly advantageous in the case of selenium rectifiers the invention may also be applied to rectiiiers utilising tellurium or other metals or metalloids in which the conversion above referred to is required.

In these and other respects the invention is not limited to the particular process above de- Having now described our invention, what we claim as new and desire to secure by Letters Patent is:

i. A process for the manufacture of an alternating current rectifier utilising an element such as selenium capable of conversion from an amorphous state into a metallic state comprising as an essential step subjecting the element to an intensive cooling treatment at a temperature or approximately -60 C. for eiiecting said conversion.

2. A. process for the manufacture of an alternating current rectifier utilising an element such as selenium capable of conversion from an amorphous state into a metallic state comprising subjecting the element in its amorphous state to the action of heat and pressuretoinitiate said conversion and thereafter cooling the element to a temperature of approximately -60 C. for completing said conversion.

3. A process for the manufacture of a selenium rectifier comprising the successive stages of applying the selenium to a base, applying pressure to said selenium at a temperature of approximately C., further heating said selenium under pressure to a temperature of approximately C. and cooling said selenium at a temperature of approximately 60 C.

4. A process for the manufacture of a selenium rectifier comprising as an essential step cooling the selenium to a temperature of approximately 60 C.

AIBERT LESLIE WILLIAMS. IESHEERNESTTHOMPSON. 

